1. Field of the Invention
This invention relates to a linear motor, wherein a magnet and a current-carrying coil are relatively and linearly moved each other, the linear motor being the most suitably applied to moving parts of an electronic equipment, such as feed mechanism of a head used in a disk player of the like.
2. Description of the Prior Art
The moving-coil type linear motor, for example, shown in FIG. 1 is well-known (cf. U.S. Pat. No. 4,439,699). In FIG. 1, a core 2 is so provided as to connect the center portions of one pair of opposite members of a box frame, namely, a yoke 1. A bobbin 4 which is surround by a coil 3 and into which the core 2 loosely fits, is movable in direction of arrow a or b. And magnets 5 and 6 which are magnetized in thickness directions thereof, are attached to the respective inside faces of the other pair of opposite members of the yoke 1.
When an electric current supplied to the coil 3 is sent through magnetic flux, the coil 3 and bobbin 4 are moved in the direction of a or b. Such a linear motor as mentioned above is used, for example, for the feed devices of optical pickups in an optical disk player or the like.
However, the above linear motor has several weak points as mentioned below:
(1) As the coil 3 is moved within a gap L.sub.g made between the magnet 5, 6 and core 2, the width of the gap L.sub.g and the thickness of the magnet 5, 6 are usually similar to each other, so that the magnetic flux density of the magnet 5, 6 becomes only about one-third to one-fourth of the residual flux density of the magnet 5, 6. Therefore, the magnetization intensity of the magnet 5, 6 are not fully utilized.
(2) Magntic flux is concentrated at the four corners of the yoke 1. Therefore, if the thickness of the yoke 1 is decided on the basis of the corner, the yoke 1 becomes rather large.
(3) As the magnetic flux generated by the current supplied to the coil 3, follows the loop formed by the yokes 1 and core 2, the self-inductance of the coil 3 becomes large, so that the electric current decreases when the bobbin is to be moved on high speed. Therefore, the thrust is reduced and the response falls away.
(4) The coil 3 is wound around the hollow bobbin 4 made of such a material as to be rather inferior in a heat conduction characteristic, so that the heat generated in the coil 3 is not evolved enough.
(5) The construction that the core 2 is fitted in the bobbin 4, makes the assembling work difficult.